1. Field of the Invention
The present invention relates, in general, to a method for forming a contact hole of a semiconductor device and, more particularly, to the use of hydrogen-containing gas as an etching gas in forming a contact hole, thereby preventing an underlying layer of a planarization layer to be damaged.
2. Description of the Prior Art
In order to better understand the background of the invention, a conventional method for forming a contact hole of a semiconductor device will be described in conjunction with FIG. 1.
Referring to FIG. 1, a semiconductor substrate 31 is provided on which two stacks of a word line 33 and a first internal insulating film 35 are formed. Then, a spacer 37 is formed at the side wall of the stack. Here, the first internal insulating film 35 and the insulating spacer 37 may be made of oxide or nitride.
Next, on the top surface of the resultant structure, a second internal insulating film 39 is deposited at a predetermined thickness, which is, then, covered with a blanket of a step coverage layer for planarization. This planarization layer 41 is typically made of an insulating layer showing good flowage while the second insulating film 39 is made of nitride. For example, spin-on-glass (hereinafter referred to as "SOG") or borophospho silicate glass (hereinafter referred to as "BPSG") may be used for the planarization layer 41.
Thereafter, a photoresist pattern (not shown) is created on the planarization layer 41 by an exposure and developing process using a contact mask (not shown). With the photoresist pattern serving as a mask, the planarization layer 41 is etched to form a contact hole 43 through which the second internal insulating film 39 is exposed. Then, the photoresist pattern is removed.
When C.sub.4 F.sub.8 and Ar are used as an etching gas for the contact hole 43, either etch stop or breakage of the second internal insulating film 39 as denoted by reference letter "a", occurs frequently. The etch stop is caused when the etching gas is used at flow rates more than a critical value since the polymer component generated at the etching process is mainly comprised of C--C bond. The breakage of the second internal insulating film results from the use of etching gas at lower flow rates than the value. The breakage of the insulating film gives rise to an increase of junction leakage current, making it difficult to form the contact hole in self-alignment.